Thursday, May 19, 2005

Time scale modification - the $0 version

A recap of yesterday's post: You can speed up speech (and music) without making people sound like chipmunks, and slow them down without making them sound like Darth Vader. This is called time scale modification. Apparently playing things faster is good for you because (1) it saves time and (2) it forces you to concentrate, so you learn better. But playing things slower can have a benefit too, when you're listening to, say, radio broadcasts in a foreign language that you're trying to learn. Often these go too fast for you to catch much, but slowing them down to 0.7-0.8xRT makes them perfect. One way to do time scale modification is to use Enounce, a plug-in for Windows Media Player and RealPlayer that lets you play stuff anywhere from 0.3-2.5xRT.

Today I'm going to look at another way of doing TSM, as it's commonly abbreviated. It's really quite easy. First, head over to and download yourself a free copy of Audacity. Audacity is open-source software for recording and editing sounds and works in Windows, Linux, OS X, you name it. It's really nifty for manipulating audio - for example, you can mash recordings up by highlighting an area of the recording and then dragging it off somewhere else. There are other free sound editors out there, too: Audacity is just the one I have installed on my computer.

Now, how to do TSM in Audacity. Select the whole recording, then go to Effect, and Change Tempo. Don't use Change Speed, that gives you chipmunks and Darth Vaders. Change Tempo shortens (or lengthens) your audio without changing the pitch - just what Enounce does. Just move the slider to where you want the speed, and press OK. It takes a few seconds to work its magic - though you can preview the effect first just to be sure that's the speed you want - and press play. Et voila! Audio speeded up or slowed down as you wish.

I don't think that the TSM effect is quite as smooth as in Enounce, which is only to be expected - this is free software, after all. There are other drawbacks, too: you can edit Ogg Vorbis, MP3 and WAV files, but nothing else - so if you have a file in .wmv format, or RealPlayer format, the only thing I can think of for you to do is to play the file and record it simultaneously in Audacity. Which pretty much defeats the purpose of the exercise in the first place. And many Internet stations encode their files in those formats. Of course, for language-learning purposes it's not so bad to listen to anything twice. Practice, practice, practice!

So I might just overcome my habitual skinflintedness and fork out $29.95 for Enounce, unless anyone knows of a way to open up files of other - proprietary - formats in Audacity or any of the other free audio editing programs, like Praat or Wavesurfer. Now that I'm running my free 7-day trial version, I don't think I could go back to listening to audio at regular speeds again. It would just be too boring.


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